Answers

Not a clematis I'm afraid. It's Passiaflora, or more commonly called The Passion Flower. Nothing to do with a rise in blood flow, but moreso the opposite, as the flower itself has been likened to the Crown of Thorns that Jesus supposedly wore. I'm sure others will explain the structure more clearly for you.

this particular one is called Passiflora incarnata - it is frost tender, tolerates down to 7 degrees C, so it's rare to find it in Britain except as an annual or under glass. It is known, though, as a very untidy grower - which is what you're complaining about! Nature of this particular plant, I'm afraid.